Which of the following statements regarding neuroendocrine tumors is FALSE?A. Tumor production of histamine and bradykinin causes vasodilation and flushing
Correct Answer: B
Carcinoid syndrome is a paraneoplastic syndrome that occurs in approximately 5% of carcinoid tumors. It is caused by endogenous secretion of serotonin, histamine, prostaglandins, and kallikrein, an enzyme that catalyzes conversion of kininogen to bradykinin. These bioactive molecules cause a wide variety of symptoms, but the most notable are diarrhea (from serotonin), flushing (from histamine and bradykinin), wheezing (from histamine and bradykinin), and cardiac lesions (from serotonin-stimulated fibrogenesis). The liver inactivates many of these bioactive molecules, and thus, it is commonly thought that carcinoid syndrome only occurs with liver dysfunction or metastasis. This is not true, as several case reports describe carcinoid syndrome in the absence of liver metastases. Carcinoid tumors were found in the lungs, ovaries, and testis, and it is thought that carcinoid syndrome may arise in these situations because of the tumors draining directly into the systemic circulation, bypassing portal circulation and subsequent inactivation. Thus, one should consider the possibility of carcinoid syndrome in the absence of liver metastases.